31. a number of, the number of

a number of 許多，謂語動詞用復數；
the number of… ……的數目，謂語動詞用單數。例：The number of students is increasing.

32. in front of, in the front of

in front of 范圍外的前面；
in the front of 范圍內的前面 例：In the front of the room sits a boy.

33. of the day, of a day

of the day 每一天的，當時的，當代的，例：a famous scientist of the day；
of a day 暫時的，不長久的。

34. three of us, the three of us

three of us 我們（不止三個）中的三個；
the three of us 我們三個（就三個人）例：The three of us - Tom, Jack and I went to the cinema.

35. by bus, on the bus

by bus 表手段，方式，不用冠詞，例：They went there by bus.
on the bus 表范圍。